For example, does this: load/unload faster than this does?: If yes, can you still load everything that that place produces in the second senario, or can you only load an amount proportional to the portion that's covered like with houses?
No, as near as I can tell resource coverage does not affect load/unload speed. Resources at a station naturally degenerate over time, so to get a higher% of hauled production, you need to have one vehicle loading at the station all the time. For part 2 of your question in one of my games, I had a station cover two coal mines with just 1 square on each, and I still transported 91% of the production.
However, one thing that does affect load/unload speed seems to be the station itself. If your train, for example, is longer than the track it seems like it takes longer to load/unload.
Also, all the cars on the train load simultaneously, so 10xoil tanker train will load more oil per 'tick' than a 5xoil train, but it takes approximately the same amount of time for both trains to reach 100% capacity (assuming enough oil at the station and it is long enough to accommodate both trains).